Heretofore, there has been a lighting device including: a step up chopper circuit that rectifies and smooths output of an AC power supply and outputs a fixed DC voltage; a step down chopper circuit that steps down the output of the step up chopper circuit and supplies the resultant voltage to a semiconductor light-emitting element; and a light modulation control circuit (refer to JP 2012-226924 A (hereinafter referred to as Document 1), for example).
In this lighting device, the light modulation control circuit controls the on-time length of a switching element included in the step down chopper circuit so as to perform light modulation control on the semiconductor light-emitting element.
In the lighting device described in Document 1, the step up chopper circuit generates a fixed voltage higher than the voltage to be applied to the semiconductor light-emitting element by rectifying and smoothing an AC voltage inputted from the AC power supply. Then, the step down chopper circuit steps down the output voltage of the step up chopper circuit to a voltage corresponding to the semiconductor light-emitting element, and supplies the resultant voltage to the semiconductor light-emitting element. Therefore, there was a problem in that, in the lighting device described in Document 1, switching loss occurred in both the step up chopper circuit and the step down chopper circuit. Also, the step up chopper circuit steps up the output voltage to the fixed voltage that is higher than the voltage to be applied to the semiconductor light-emitting element, and therefore large circuit components having high breakdown voltage need to be used in the step up chopper circuit and the step down chopper circuit, and therefore there was also a problem in that the lighting device increases in size.